## Lecture 18 , 19 and 20 :- OPAMPS Design

Common Data : VDD = 1.8V , Lmin  = 0.18µm, µ0N = 350cm2/V s, µ0P  = 100cm2/V s, |VTH | = 0.55, tox = 3.8nm, λ = 0.07V−1, χ = 0.1.

1. Consider the amplifier in Fig. 27, where of the transistors are and that of are Given 1. Calculate the poles at nodes and , if and Also calculate the phase margine for unity gain feedback.
2. How will you redesign the amplifier to have a phase margine of ?
3. Calculate the slew rate of the opamp for b part only. Figure 27: Figure for Question 1

2. An amplifier has forward gain of with two poles at and frequencies.

1. For find the phase margine with unity gain feedback if
1. 2. 3. 2. If the unity gain closed loop amplifier exhibits a frequency peaking of near the gain crossover frequency, then what is the phase margine?

3. Consider the circuit shown in Fig. 28

1. What is the advantage of using transistors and ?
2. Determine the of the opamp .
3. Derive the maximum output swing
4. Derive the value of needed for a phase margine of 60o  at unity gain feedback when 5. Determine the slew rate of the opamp Figure 28 : Figure for Question 3

4. Consider the opamp shown in Fig. 29 Figure 29 : Figure for Question 4

1. Calculate the gain of opamp if and for
1. 2. 3. 2. Calculate the output swing of the opamp
3. Calculate slew rate if and 1. and 2. and 5.Design a PMOS input stage two stage opamp. The specifications to be met are      ,  . Assume and stability needed is 6.Consider the amplifier shown in Fig. 30 employing a cascode stage as a amplifier. Assume node is dominant. Sketch the frequency response and explain how the circuit can be compensated . Figure 30: Figure for Question 6

1. If the circuit is modified as shown in Fig. 31, then sketch the frequency response for Figure 31: Figure for Question 6

1. 2. 3. 1. If the circuit is modified as shown in Fig. 32, then sketch the frequency response for and Figure 32: Figure for Question 6

1. 2. 3. 